Advances in monolithic materials for sample preparation in drug and pharmaceutical analysis

Monolith-coated microcentrifuge tubes for the easy extraction of psychoactive substances from urine samples and liquid chromatography-tandem mass spectrometry determination

BACKGROUND

Sample extraction is one of the most critical steps in most of the analytical processes. Nowadays, there is a demand for simple approaches that can effectively extract and concentrate target analytes from complex matrices, like biofluids, with accurate and reliable results.

RESULTS

A porous monolith of poly(methacrylic acid-co-ethylene glycol dimethacrylate) has been immobilized on the inner wall of a 2 mL commercial polypropylene microcentrifuge tube through radical photopolymerization, using bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide as radical initiator and 405 nm laser pointer activation. Photopolymerization parameters were adjusted to obtain a continuous and homogeneous polymer layer (0.16 mm wet polymer thickness and 31 mg dry polymer weight) in the inner tube surface. Extraction efficiency of twelve psychoactive substances was assessed by the evaluation of the effect of sample pH, extraction and desorption times, and desorption solvent volume. Moreover, matrix effect, reusability and stability of monolith-coated microcentrifuge tubes were studied. Sample extracts were measured by liquid chromatography-tandem mass spectrometry, providing limits of quantification (LOQ) from 0.2 to 2.7 μg L-1, recoveries from 80 to 118 %, relative standard deviations lower than 17 %, and a linear range from LOQ to 500 μg L-1.

SIGNIFICANCE

The proposed device is suitable for the easy and simple extraction of psychoactive substances from urine samples with a high portability, reduced solvent consumption, low cost, and low environmental impact.

Organic-silica hybrid monolithic sorbents for sample preparation techniques: A review on advances in synthesis, characterization, and applications

Organic-silica hybrid monolithic materials have attracted considerable attention as potential stationary phases in separation science. These materials combine the advantages of organic polymer and silica-based monoliths, including easy preparation, lower back pressure, high permeability, excellent mechanical strength, thermal stability, and tunable surface chemistry with high surface area and selectivity. The outstanding chromatographic efficiency as stationary phase of hybrid monolithic capillary columns for capillary liquid chromatography and capillary electrochromatography has been reported in many papers. Organic-silica hybrid monolithic materials have also been extensively used in the field of sample preparation. Owing to their surface functionalities, these porous sorbents offer unique selectivity for pre-concentration of different analytes in the most complex matrixes by fast dynamic transport. These sorbents not only improve the analytical method sensitivity, but also introduce novelties in terms of extraction devices and instrument coupling strategies. The current review covers the period spanning from 2017 to 2023 and describes the properties of organic-inorganic hybrid monolithic materials, the present status of this technology and summarizes recent developments in their use as innovative sorbents for microextraction sample preparation techniques (solid phase microextraction with pipette tip, offline in-tube SPME, in-tube SPME online with LC, and in-tube SPME directly coupled with mass spectrometry). Aspects such as the synthesis methods (sol-gel process, one-pot approach, and polyhedral oligomeric silsesquioxanes-based procedure), characterization techniques, and strategies to improve extraction efficiency in various applications in different areas (environmental, food, bioanalysis, and proteomics) are also discussed.

Sponge-nested polymer monolith sorptive extraction

Polymer monoliths are an alternative to traditional particle-packed supports used in solid-phase extraction because of their ease of preparation, high porosity, and pH stability. They often required the attachment of monoliths to a support, such as the internal walls of a column to enable their use for sample preparation. Applications of free-standing polymer monoliths are rarely found because of their limited mechanical stability. Herein, divinylbenzene monoliths were polymerised within a commercial melamine-formaldehyde sponge using different polymerisation times. The sponge-nested polymer monoliths are highly robust, and their size and shape can be easily adjusted for desired applications. The prepared sponge-nested polymer monoliths had surface areas in the range of 237 m² g^-1 to 369 m² g^-1. A melamine-formaldehyde sponge cut into 1 cm³ cubes were used to template the polymer monoliths. Miniaturized monoliths with a size of 0.125 cm³ were directly cut from the larger cubes without compromising the integrity of the porous monolith structure. The resulting nested monolith sorptive extraction (NMSE) supports were applied for the extraction of the endocrine disruptors bisphenol A, 4-tert-butylphenol, and 4-tert-octylphenol. The prepared sponge-nested monoliths are low-cost (40 monoliths/AU$). NMSE was carried out by the direct immersion of the monoliths in the aqueous standards/samples, requiring only an orbital shaker for the extraction procedure. Best performance was obtained for polymer monoliths polymerized for 6 h, enabling limits of detection of 5.6 to 6.5 µg L^-1 for the selected analysis using HPLC-UV.

Determination of polycyclic aromatic hydrocarbons in surface waters by high performance liquid chromatography previous to preconcentration through solid-phase extraction by using polymeric monoliths

A simple, sensitive and reproducible solid-phase extraction method using plastic cartridges containing a monolithic sorbent (m-SPE), coupled to reverse phase liquid chromatography analysis, aiming to determine fifteen polycyclic aromatic hydrocarbons in surface water samples, was developed. The sorbent was easily prepared through a thermal polymerization reaction by using a mixture of n-butyl methacrylate as non-polar monomer and ethylene glycol dimethacrylate as crosslinker contained in a typical Polypropylene syringe cartridge. The effect of different parameters (type of hydrophobic monomer, elution solvent, sample volume, sorbent amount and sorbent load capacity) on the extraction efficiency was optimized. The optimal conditions were achieved by using n-butyl methacrylate as monomer, tetrahydrofurane (THF) as solvent for sorbent cleaning, THF:acetone (1:1) as elution solvent, 25.00 mL of sample volume, 600 µL of the polymerization mixture and 60 µg L^-1 as sample loading capacity. Finally, the sorbent charge capacity, the reusability of the cartridges and the extraction efficiency of the m-SPE monolith, as compared with a typical C8 cartridge, were evaluated. Under the optimized experimental conditions, enrichment factors were between 76 and 103, relative recovery factors from 78 to 103%, accuracy values in the range of 58 to 98%, and inter-batch reproducibility values from between 2 and 10%, were obtained. The limits of detection and quantification were obtained by two different procedures: the signal to noise (S/N) ratios (3 and 10, respectively) and the IUPAC convention. The lowest LOD and LOQ values, obtained with the S/N ratios, were between 0.02 and 1.00 µg L^-1, respectively whereas with the IUPAC convention the values were between 0.07 and 5 µg L^-1. Using this procedure, several PAHs could be detected in the surface water sample taken from a river stream located in La Plata city (Buenos Aires Province, Argentina).

Novel chemically cross-linked self-molding particulate sorbents as solid-phase extraction media

Here, we describe novel, chemically cross-linked, self-molding particulate polymer sorbents that are utilized as a molding-type solid-phase extraction medium (M-SPEM), which exhibits high permeability and rigidness. To fabricate such M-SPEM, first, polyethyleneimine (PEI)-modified reversed-phase (RP)-type particulate sorbents were synthesized, thereafter, they were chemically cross-linked by a polymer having many epoxy groups together with additional PEI. By optimizing the binding conditions of the particulate sorbents, the resultant M-SPEM has almost the same adsorption properties as the corresponding unmolded particulate sorbent for some polar (e.g., uracil and adenine) compounds. The binding technique proposed here is expected to facilitate the fabrication of molding-type sorbents and improve the performance of the SPE procedure.

Unique On-Site Spinning Sampling of Highly Water-Soluble Organics Using Functionalized Monolithic Sorbents

Water utilities encounter unpredictable odor issues that cannot be explained by routine water parameters during spring runoff, even in the summer and fall. Highly water-soluble organics (e.g., amino acids and saccharides) have been reported to form odorous disinfection byproducts during disinfection, but the lack of simple and practical on-site sampling techniques hampers their routine monitoring at trace levels in source water. Therefore, we have created two functionalized nested-in-sponge silica monoliths (NiS-SMs) using a one-pot synthesis method and demonstrated their application for extracting highly soluble organics in water. The NiS-SMs functionalized with the sulfonic group and phenylboronic moiety selectively extracted amino acids and monosaccharides, respectively. We further developed a spinning sampling technique using the composites and evaluated its robust performance under varying water conditions. The spinning sampling coupled to high-performance liquid chromatography tandem mass spectrometry analysis provided limits of detection for amino acids at 0.038-0.092 ng L^-1 and monosaccharides at 0.036-0.14 ng L^-1. Using the pre-equilibrium sampling-rate calibration, we demonstrated the applicability of the spinning sampling technique for on-site sampling and monitoring of amino acids and monosaccharides in river water. The new composite materials and rapid on-site sampling technique are unique and efficient tools for monitoring highly soluble organics in water sources.

Facile fabrication of functional groups-rich sorbent for the efficient enrichment of aromatic N- and S-containing compounds in environmental waters

Extraction strategy is designed for the pretreatment of low contents of aromatic N- and S-containing compounds (ANSCs) in environmental waters prior to chromatographic analysis. To enrich studied ANSCs effectively, poly (9-vinylanthracene/4-vinylphenylboronic acid-co-ethylene dimethacrylate/divinylbenzene) polymeric monolithic sorbent were facilely fabricated using the one-step free radical polymerization. Various technologies were employed to investigate the structure and morphology of the resultant monolith. Combining with solid-phase microextraction format, the sorbent exhibited satisfying concentrated performance for ANSCs through multiply interactions under the optimized conditions. After desorption with eluent, the retained analytes were analyzed by HPLC. Results showed that the extraction efficiencies ranged from 51.6 to 93.2%. The linear ranges and limits of detection were 0.01-150 μg/L and 0.63-2.64 ng/L, respectively. Furthermore, the precisions were all below 10%. The introduced approach was productively practiced on three real water samples for simultaneous quantification of studied ANSCs, and the fortified recoveries ranged from 81.5 to 118%. All the results well evidenced that prepared sorbent can enrich ANSCs effectively and the introduced method is reliable alternative for routine analysis of ANSCs in environmental waters.

Fast preparation of hybrid monolithic columns via photo-initiated thiol-yne polymerization for capillary liquid chromatography

Although several approaches have been developed to fabricate hybrid monoliths, it would still take a few hours to finish the formation of monoliths. Herein, photo-initiated thiol-yne polymerization was first adopted to in situ fabricate hybrid monoliths within the confines of UV-transparent fused-silica capillary. A silicon-containing diyne (1,3-diethynyltetramethyl-disiloxane, DYDS) was copolymerized with three multithiols, 1,6-hexanedithiol, trimethylolpropane tris(3-mercaptopropionate) and pentaerythriol tetrakis(3-mercaptopropionate), by using a binary porogenic system of diethylene glycol diethyl ether (DEGDE)/poly(ethylene glycol) (PEG200) within 10 min. Several characterizations of three hybrid monoliths (assigned as I, II and III, respectively) were performed. The results showed that these hybrid monoliths possessed bicontinuous porous structure, which was remarkably different from that via typical free-radical polymerization. The highest column efficiency of 76,000 plates per meter for butylbenzene was obtained on the column I in reversed-phase liquid chromatography (RPLC). It was observed that the efficiencies for strong-retained butylbenzene were almost close to those of weak-retained benzene, indicating a retention-independent efficient performance of small molecules on hybrid column I. The surface area of this hybrid monolith was very small in the dry state (less than 10.0 m²/g), and the chromatographic behavior of hybrid monolithic columns would be possibly explained by radical-mediated step-growth process of thiol-yne polymerization. Finally, the column I was applied for separation of BSA tryptic digest by cLC-MS/MS, indicating satisfactory separation ability for complicated samples.

Sol-gel niobia sorbent with a positively charged octadecyl ligand providing enhanced enrichment of nucleotides and organophosphorus pesticides in capillary microextraction for online HPLC analysis

A niobia-based sol-gel organic-inorganic hybrid sorbent carrying a positively charged C₁₈ ligand (Nb₂ O₅ -C₁₈ (+ve)) was synthesized to achieve enhanced enrichment capability in capillary microextraction of organophosphorus compounds (which include organophosphorus pesticides and nucleotides) before their online analysis by high-performance liquid chromatography. The sorbent was designed to simultaneously provide three different types of molecular level interactions: electrostatic, Lewis acid-base, and van der Waals interactions. To understand relative contributions of various molecular level analyte-sorbent interactions in the extraction process, two other sol-gel niobia sorbents were also created: (a) a purely inorganic sol-gel niobia sorbent (Nb₂ O₅ ) and (b) an organic-inorganic hybrid sol-gel niobia sorbent carrying an electrically neutral-bonded octadecyl ligand (Nb₂ O₅ -C₁₈ ). The extraction efficiency of the created sol-gel niobia sorbent (Nb₂ O₅ -C₁₈ (+ve)) was compared with that of analogously designed and synthesized titania-based sol-gel sorbent (TiO₂ -C₁₈ (+ve)), taking into consideration that titania-based sorbents present state-of-the-art extraction media for organophosphorus compounds. In capillary microextraction with high-performance liquid chromatography analysis, Nb₂ O₅ -C₁₈ (+ve) had shown 40-50% higher specific extraction values (a measure of extraction efficiency) over that of TiO₂ -C₁₈ (+ve). Compared to TiO₂ -C₁₈ (+ve), Nb₂ O₅ -C₁₈ (+ve) also provided superior analyte desorption efficiency (96 vs. 90%) during the online release of the extracted organophosphorus pesticides from the sorbent coating in the capillary microextraction capillary to the chromatographic column using reversed-phase high-performance liquid chromatography mobile phase.

Optimization and application of octadecyl-modified monolithic silica for solid-phase extraction of drugs in whole blood samples

Monolithic silica in MonoSpin for solid-phase extraction of drugs from whole blood samples was developed to facilitate high-throughput analysis. Monolithic silica of various pore sizes and octadecyl contents were synthesized, and their effects on recovery rates were evaluated. The silica monolith M18-200 (20μm through-pore size, 10.4nm mesopore size, and 17.3% carbon content) achieved the best recovery of the target analytes in whole blood samples. The extraction proceeded with centrifugal force at 1000rpm for 2min, and the eluate was directly injected into the liquid chromatography-mass spectrometry system without any tedious steps such as evaporation of extraction solvents. Under the optimized condition, low detection limits of 0.5-2.0ngmL^-1 and calibration ranges up to 1000ngmL^-1 were obtained. The recoveries of the target drugs in the whole blood were 76-108% with relative standard deviation of less than 14.3%. These results indicate that the developed method based on monolithic silica is convenient, highly efficient, and applicable for detecting drugs in whole blood samples.

Micro-SPE in pipette tips as a tool for analysis of small-molecule drugs in serum

AIM

Micro-SPE in pipette tips (μ-SPE-PT) with particle sorbent has never been used in small-molecule drug analysis. Methodology & results: μ-SPE-PT was used for the extraction of statins from biological materials followed by UHPLC-MS/MS. The commercial and homemade μ-SPE-PT tips filled with particle sorbent were compared. While the homemade tips enabled direct serum sample loading into the sorbent, protein precipitation (PP) had to be implemented before μ-SPE-PT procedure using commercial tips. Three μ-SPE-PT methods were developed and validated: method A: μ-SPE-PT with homemade tips; method B: PP + μ-SPE-PT with homemade tips; and method C: PP + μ-SPE-PT with commercial tips. Method A enabled a simple high-throughput approach (48 samples in 90 min) compared with methods B and C that required three-times longer time. However, PP increased the recoveries of protein-bound analytes and extracts purity in methods B and C. The matrix effects without internal standards correction for method C were significantly higher than those for the methods A and B.

CONCLUSION

Compared with commercial tips, homemade tips filled with particles were found to be more suitable for drug analysis. Commercial tips tested in this study were found challenging but the conditions under which they could be applicable were also defined.

Metal-Organic Framework-Polymer Composite as a Highly Efficient Sorbent for Sulfonamide Adsorption and Desorption: Effect of Coordinatively Unsaturated Metal Site and Topology

In this study, we first demonstrated the effect of two types of metal-organic framework-polymer (MOF-polymer) monoliths on in-tube solid-phase microextraction (IT-SPME) of sulfonamides. Sulfonamides were successfully adsorbed onto MIL-101(Cr)-polymer but were difficult to elute due to these sulfonamides could interact via Lewis acid-base interaction with the presence of Cr(III) coordinatively unsaturated metal sites (CUS). Moreover, the cage-type topology of MIL-101(Cr) that could produce multiple pathways thus complicates the desorption of the test analytes from the sorbent. Contrastingly, MIL-53(Al)-polymer provided weaker Al(III) CUS, and its one-dimensional channel pore structure could provide an unhindered pathway for sulfonamides transfer during elution. After optimizing the IT-SPME condition such as MOF content, pH of sample matrix, column length, extraction flow rate, and elution volume, the calculated extraction recovery of sulfonamides in MIL-53(Al)-polymer as analyzed by microemulsion electrokinetic chromatography (MEEKC) were in the range of 40%-90% with relative standard deviations (RSDs) below 5% and a reusability of at least 30 times.

Solid-phase extraction based on ground methacrylate monolith modified with gold nanoparticles for isolation of proteins

In this study, a novel polymeric material functionalized with gold nanoparticles (AuNPs) was prepared as solid-phase extraction (SPE) sorbent for isolation of proteins. The sorbent was synthesized from a powdered poly(glycidyl-co-ethylene dimethacrylate) monolith, and modified with ammonia, followed by immobilization of AuNPs on the pore surface of the material. To evaluate the performance of this SPE support, proteins were selected as test solutes, being the extraction conditions and other parameters (loading capacity and regenerative ability of sorbent) established. The results indicated that this sorbent could be employed to selectively capture proteins according to their pI, on the basis of the strong affinity of these biomacromolecules towards to AuNPs surface. The applicability of this sorbent was demonstrated by isolating protein species of interest (bovine serum albumin, cytochrome c and lectins in European mistletoe leaves), followed by SDS-PAGE analysis.

Spin column extraction as a new sample preparation method in bioanalysis

Sample preparation is important in obtaining accurate data for qualification and quantification in bioanalysis. We have recently focused on monolithic silica for high-throughput analysis. These extraction processes - using monolithic silica packed in spin column - such as sample loading, washing and elution, are executed by centrifugation. There are several possibilities such as on-column derivatization for the determination of amines or carboxylic acids in the sample. The spin column extraction reduces the sample preparation time required for determination of drugs and other chemicals in biological materials and increases productivity in bioanalysis. We expect spin column extraction to become the mainstream method of sample processing in the future.

Determination of imidazole derivatives by micellar electrokinetic chromatography combined with solid-phase microextraction using activated carbon-polymer monolith as adsorbent

In this study, an effective method for the separation of imidazole derivatives 2-methylimidazole (2-MEI), 4- methylimidazole (4-MEI) and 2-acetyl-4-tetrahydroxybutylimidazole (THI) in caramel colors using cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-sweeping-MEKC) was developed. The limits of detection (LOD) and quantitation (LOQ) for the CSEI-sweeping-MEKC method were in the range of 4.3-80μgL(-1) and 14-270μgL(-1), respectively. Meanwhile, a rapid fabrication activated carbon-polymer (AC-polymer) monolithic column as adsorbent for solid-phase microextraction (SPME) of imidazole colors was developed. Under the optimized SPME condition, the extraction recoveries for intra-day, inter-day and column-to-column were in the range of 84.5-95.1% (<6.3% RSDs), 85.6-96.1% (<4.9% RSDs), and 81.3-96.1% (<7.1% RSDs), respectively. The LODs and LOQs of AC-polymer monolithic column combined with CSEI-sweeping-MEKC method were in the range of 33.4-60.4μgL(-1) and 111.7-201.2μgL(-1), respectively. The use of AC-polymer as SPME adsorbent demonstrated the reduction of matrix effect in food samples such as soft drink and alcoholic beverage thereby benefiting successful determination of trace-level caramel colors residues using CSEI-sweeping-MEKC method. The developed AC-polymer monolithic column can be reused for more than 30 times without any significant loss in the extraction recovery for imidazole derivatives.